Whether or not obesity should be considered a disease on its own, it is also an important risk factor for many chronic physical and mental illnesses.[1] The generally accepted view is that being overweight causes similar health problems to obesity, but to a lesser degree.

More than 85% of those with hypertension have a BMI greater than 25.[6] The risk of hypertension is 5 times higher in the obese as compared to those of normal weight. A definitive link between obesity and hypertension has been found using animal and clinical studies, which have suggested that there are multiple potential mechanisms for obesity-induced hypertension. These mechanisms include the activation of the sympathetic nervous system as well as the activation of the renin–angiotensin-aldosterone system.[7] The association between hypertension and obesity has been also well described in children.[8]

One of the strongest links between obesity and disease is that with type 2 diabetes. These two conditions are so strongly linked that researchers in the 1970s started calling it “diabesity”.[6] Excess weight is behind 64% of cases of diabetes in men and 77% of cases in women.[14]

Obesity leads to infertility in both men and women. This is primarily due to excess estrogen interfering with normal ovulation in women[6] and altering spermatogenesis in men.[16] It is believed to cause 6% of primary infertility.[6][17] A review in 2013 came to the result that obesity increases the risk of oligospermia and azoospermia in men, with an of odds ratio 1.3.[18] Being morbidly obese increases the odds ratio to 2.0.[18]

Ischemic stroke is increased in both men and women who are obese.[6] For women with a BMI greater than 30, the risk of ischemic stroke increases by 1.7 fold,[25] while men with a BMI greater than 30 had a risk of stroke 2.0 times greater.[26]

Many cancers occur at increased frequency in those who are overweight or obese. A study from the United Kingdom found that approximately 5% of cancer is due to excess weight.[33] These cancers include: [34]

Al high body mass index (BMI) is associated with a higher risk of developing ten common cancers including 41% of uterine cancers and at least 10% of gallbladder, kidney, liver and colon cancers in the UK.[35]

Risk of suicide decreases with increased body mass index in the United States.[36]

Obesity has been associated with depression.[6] The relationship is strongest in those who are more severely obese, those who are younger, and in women.[37] Suicide rate however decreases with increased BMI.[36]

Obesity is associated with a number of chronic lung diseases, including asthma and COPD.[39] It is believed that a systemic pro-inflammatory state induced by some causes of obesity may contribute to airway inflammation, leading to asthma.[41]

Increased rates of arthritis are seen in both weight-bearing and non-weight-bearing joints.[6] Those with a BMI greater than 26.4 had rate of osteoarthritis of the knees 6 times greater than those with a BMI of less than 23.4, well rates of osteoarthritis in the hand was about 1.5 times greater.[45]

Urge, stress, and mixed incontinence all occur at higher rates in the obese.[48] The rates are about double that found in the normal weight population.[49] Urinary incontinence improves with weight lost.[50]